How did the Breton succession dispute involve Edward III and Philip VI?

The Breton succession dispute, which began in 1341 following the death of Duke John III, became a significant theater of the Hundred Years’ War because it drew in the rival interests of Edward III and Philip VI of France.12

The conflict arose between two claimants: Charles of Blois, who was the nephew of Philip VI, and John of Montfort, who sought English support. Philip VI naturally favored his nephew and successfully captured John of Montfort at Nantes in 1341. In response, Edward III—who claimed suzerainty over Brittany—provided military support to the Montfortist cause, leading to direct confrontations between English and French forces within the duchy.12

By December 1342, armies representing both kings were poised for battle near Vannes, though papal intervention eventually led to the Truce of Malestroit. The struggle continued for years, exemplified by the famous Combat of the Thirty in 1351, until the house of Montfort eventually secured the duchy.134